The maturation of nerve cells from chick embryos will be analyzed using low density cell culture conditions. The role of extracellular factors such as adhesivity with the substratum will be investigated with respect to rates of axon elongation, branching frequencies of axons, rates of protein synthesis in nerve cell bodies, and the capacity of nerves to form controlled shapes. Ability of parasympathetic nerves to respond to attractive influences from target organs, and of sensory nerves to reach sensory hairs in lips of mouse embryos will be investigated using organ culture procedures. Scanning electron microscopy of single cells, of nerves innervating target organs and hairs, and of various organs undergoing morphogenesis will be carried out. Cell surface dynamics during axon elongation and epithelial cell morphogenesis will be investigated using scanning and transmission electron microscopy and employing cell surface marking agents recognizable with those techniques. The experiments during the proposed research period are intended to increase our knowledge about both single cell and multicellular morphogenesis in avian and mammalian embryos.